Fiber optic drop cable

ABSTRACT

A fiber optic cable includes a subunit and an outer portion. The subunit includes a subunit jacket defining a passageway interior thereto, an optical fiber extending through the passageway, and a first reinforcement material constraining the optical fiber within the subunit jacket such that the optical fiber and the subunit jacket are coupled to one another by way of the first reinforcement material. The outer portion of the fiber optic cable includes an outer jacket defining an outer periphery of the cable and a second reinforcement material between the outer jacket and the subunit jacket. The second reinforcement material includes fiberglass yarn, and hoop stress applied to the fiberglass yarn by the outer jacket constrains the fiberglass yarn such that it is positioned and oriented to provide anti-buckling support to the fiber optic cable and mitigate effects on the optical fiber of jacket shrinkage due to low temperatures.

BACKGROUND

Aspects of the present disclosure relate generally to a fiber opticcable configured for use in fiber-to-the-home (FTTH) applications orother applications.

A “drop cable” is typically designed for connecting optical fibers froma larger network, outside a home or business, to a local network of ahome or business. The drop cable may carry one or a small number ofoptical fibers, and may further be designed to fully support its ownweight when strung through the air. Further the drop cable may bedesigned to withstand the elements of wind, rain, and ice, whilemitigating the effects on the optical fibers of shrinking or expandingof the cable due to axial loading, cold-temperatures, or other causes.In addition, the drop cable should be narrow or small enough to easilypass through small tunnels or ducts (e.g., an inch- or even ahalf-inch-diameter duct), as may be used in fiber-to-the-homeapplications.

To accomplish some or all such tasks, the drop cable may include rigidstrength members, such as glass-reinforced plastic (GRP) or steel rods.The rods provide tensile strength and oppose buckling. However, the rodsmay limit flexibility of the cable and may also be difficult to cutthrough and remove should a portion of the cable jacket need to beremoved during the installation of the optical fiber and associatedhardware. Accordingly, a need exists for a fiber optic cable that issome or all of a small or narrow fiber optic drop cable havingtensile/anti-buckling ruggedness and weather-ability, but with improvedflexibility and access to the optical fibers.

SUMMARY

One embodiment relates to a fiber optic cable that includes a subunitand an outer portion. The subunit includes a subunit jacket defining apassageway interior thereto, an optical fiber extending through thepassageway, and a first reinforcement material constraining the opticalfiber within the subunit jacket such that the optical fiber and thesubunit jacket are coupled to one another by way of the firstreinforcement material. The outer portion of the fiber optic cableincludes an outer jacket defining an outer periphery of the cable and asecond reinforcement material between the outer jacket and the subunitjacket. The second reinforcement material includes fiberglass yarn, andhoop stress applied to the fiberglass yarn by the outdoor jacket axiallyconstrains the fiberglass yarn such that the fiber glass yarn ispositioned and oriented to provide anti-buckling support to the fiberoptic cable and mitigate effects on the optical fiber of jacketshrinkage due to low temperatures.

Another embodiment relates to a fiber optic cable that includes asubunit and an outer jacket. The subunit includes a subunit jacketdefining a passageway interior to the subunit jacket, one or moreoptical fibers extending through the passageway, and a firstreinforcement material constraining the optical fiber(s) within thesubunit jacket such that the optical fiber(s) and the subunit jacket arecoupled to one another by way of frictional contact or adhesion with thefirst reinforcement material. The first reinforcement material is atleast one of (i) so positioned and (ii) non-rigid in bending, such thatthe subunit has essentially no bend preference (e.g., substantially nobend preference; a bend preference less than the ratio of 2:1, 1.5:1, or1.25:1). The outer portion of the fiber optic cable includes an outerjacket defining an outer periphery of the cable, which may include askin or a composite structure. A second reinforcement material isbetween the outer jacket and the subunit jacket, where the secondreinforcement material is at least one of so positioned and non-rigid inbending such that, in combination with the subunit, the fiber opticcable has essentially no bend preference. The second reinforcementmaterial includes fiberglass yarn, and hoop stress applied to thefiberglass yarn by the outdoor jacket axially constrains the fiberglassyarn between the subunit and outer jackets such that the fiberglass yarnis held in position and oriented to provide anti-buckling support to thefiber optic cable and thereby mitigate effects on the optical fiber ofjacket shrinkage due to low temperatures experienced by the fiber opticcable.

Other embodiments includes methods of manufacturing such a fiber opticcable. One such method includes a step of pressure-extruding (e.g., at100 bar or more) the outer jacket over the second reinforcement materialto tightly constrain components of the fiber optic cable interior to theouter jacket. Another such method includes a step of tensioning theoptical fiber while extruding the subunit jacket about firstreinforcement material and the optical fiber so that the optical fiberis without excess fiber length following cooling and shrinkage of thesubunit jacket after extruding the subunit jacket.

Yet another embodiment includes a fiber optic cable including indoor andoutdoor jackets, an optical fiber, first and second reinforcementmaterials, and material discontinuities in the outdoor jacket. Theindoor jacket defines a passageway interior thereto and the opticalfiber extends through the passageway of the indoor jacket. Furthermore,the indoor jacket includes a flame-retardant jacketing material and isconfigured for indoor operation (e.g., plenum- or riser-rated). Thefirst reinforcement material constrains the optical fiber within theindoor jacket such that the optical fiber and indoor jacket are coupledto one another by way of the first reinforcement material. The outdoorjacket defines an outer periphery of the cable, and the outdoor jacketincludes a medium- or high-density polyethylene and is configured foroutdoor operation (e.g., blocks ultra-violet light). The materialdiscontinuities in the outdoor jacket provide lengthwise paths fortearing open the outdoor jacket to access the indoor jacket. The secondreinforcement material is embedded in or bonded to the outdoor jacketsuch that second reinforcement material remains attached to the outdoorjacket when the outdoor jacket is torn open via the materialdiscontinuities. Either the second reinforcement material isnon-stranded or the material discontinuities spiral lengthwise along theoutdoor jacket such that lay lengths of the material discontinuities andthe reinforcement material match one another (e.g., the materialdiscontinuities overlay the interface between individual yarns of thesecond reinforcement material). Accordingly, the outdoor jacket may betorn open by way of the discontinuities to access the indoor jacket withat least a portion of the second reinforcement material simultaneouslycontrolled and moved out of the way for accessing the indoor jacket.

Additional features and advantages are set forth in the DetailedDescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings. It is to be understood that both theforegoing general description and the following Detailed Description aremerely exemplary, and are intended to provide an overview or frameworkto understand the nature and character of the claims.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying Figures are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiments, andtogether with the Detailed Description serve to explain principles andoperations of the various embodiments. As such, the disclosure willbecome more fully understood from the following Detailed Description,taken in conjunction with the accompanying Figures, in which:

FIG. 1A is a sectional view of a fiber optic cable according to anexemplary embodiment.

FIG. 1B is a top-perspective digital image showing a sectional view ofthe fiber optic cable of FIG. 1A.

FIG. 2 is a side-view digital image of the fiber optic cable of FIG. 1with the outer jacket partially open to show aramid fibers andfiber-glass yarns beneath the outer jacket.

FIG. 3 is a side-view digital image of the fiber optic cable of FIG. 1showing a subunit extending from between the yarns.

FIG. 4 is a side-view digital image of the subunit of FIG. 3 with theend opened to show aramid fibers and a tight-buffered optical fiberextending from a subunit jacket.

FIG. 5 is a front-perspective-view digital image of the fiber opticcable of FIG. 1 with the outer jacket being peeled open via materialdiscontinuities in the outer jacket.

FIG. 6 is a graphical representation of attenuation versus time withrespect to changes in temperature for the cable of FIGS. 1-5.

FIGS. 7-9 are perspective views of fiber optic cables according to otherexemplary embodiments.

DETAILED DESCRIPTION

Before turning to the following Detailed Description and Figures, whichillustrate exemplary embodiments in detail, it should be understood thatthe present invention is not limited to the details or methodology setforth in the Detailed Description or illustrated in the Figures. Forexample, as will be understood by those of ordinary skill in the art,features and attributes associated with embodiments shown in one of theFigures or described in the text relating to one of the embodiments maywell be applied to other embodiments shown in another of the Figures ordescribed elsewhere in the text.

Referring to FIG. 1A as well as FIGS. 1B-5, a fiber optic cable 110includes a subunit 112 and an outer portion 114. The subunit 112includes a subunit jacket 116 (e.g., sheath) defining a passageway 118interior thereto, an optical fiber 120 extending through the passageway118, and a first reinforcement material 122 (e.g., strength material,strength member, aramid fibers or yarns) constraining the optical fiber120 within the subunit jacket 116 such that the optical fiber 120 andthe subunit jacket 116 are coupled to one another by way of the firstreinforcement material 122.

In some embodiments, the subunit jacket 116 is pressure extruded (e.g.,extruded at a pressure of at least 100 bar; no more than 200 bar) overthe first reinforcement material 122, which subsequently cools andshrinks to tightly constrain the first reinforcement 122 and the opticalfiber 120. Frictional interfaces between the first reinforcementmaterial 122 and the subunit jacket 116 and between the firstreinforcement material 122 and optical fiber 120 provide couplingbetween the subunit jacket 116 and the optical fiber 120. In otherembodiments, an adhesive is used to couple the subunit jacket 116 andoptical fiber 120 by way of the first reinforcement material 122. Instill other embodiments, the subunit jacket 116 and optical fiber 120are otherwise coupled, with or without inclusion or support fromreinforcement material.

Still referring to FIG. 1, the outer portion 114 of the fiber opticcable 110 includes an outer jacket 124 defining an outer periphery 126(e.g., exterior surface, outside perimeter in round embodiments) of thecable 110 and a second reinforcement material 128 between the outerjacket 124 and the subunit jacket 116. In some embodiments, the secondreinforcement material 128 includes fiberglass yarn 130, and hoop stress(shown as arrows 132 in FIG. 1) applied to the fiberglass yarn 130 bythe outer jacket 124 constrains the fiberglass yarn 130 (i.e., holds thefiberglass yarn 130 in a generally fixed position and orientation withrespect to the cable 110).

According to an exemplary embodiment, the fiber glass yarn 130 ispositioned and oriented to provide anti-buckling support to the fiberoptic cable 110 and to mitigate effects of jacket shrinkage due to lowtemperatures on the optical fiber 120. More specifically, the fiberglassyarn 130 may be aligned with the length of the fiber optic cable 110,having no lay length; or may alternatively be stranded around thesubunit 112 (i.e., wound), such as helically or S-Z stranded, with a laylength or average lay length of at least 100 mm, such as at least 200mm, where the lay length is the lengthwise distance along the cable 110for one cycle of the corresponding winding pattern (e.g., one fullhelical wrap around the subunit 112).

Use of flexible (yet constrained) fiberglass yarn 130 in the secondreinforcement material 128 may overcome stiffness problems associatedwith glass-reinforced plastic rods, steel rods, and other strengthmembers discussed in the Background section, while the fiberglass yarnis held positioned and oriented to provide anti-buckling reinforcement.Hoop stress from the outer jacket holds the fiberglass yarn 130 in placeso that the individual fibers of the yarn 130 work together to provideanti-buckling strength in the lengthwise direction of the cable 110,without a solid resin material to bind the individual fibers of the yarn130 to one another. Instead, the individual fibers of the fiberglassyarn 130 are generally able to move relative to one another as the cablebends, which allows for improved flexibility of the fiber optic cable110. In some embodiments, the fiberglass yarn 130 includes a non-rigidbinding material, such as cohesive polymers or an extremely low-density,smooth, soft coating, to clump the fibers together in flattened strips(e.g., generally flat, see FIG. 1), as is the case withcommercially-available fiberglass yarns sold under the product codeFVAPW1200 manufactured by Gotex S.A. (water blocking coated fiberglassyarn, 1.250 TEX). In some embodiments, the coating may includewater-blocking additives (e.g., super-absorbent polymers).

According to an exemplary embodiment, the first reinforcement material122 includes (e.g., is formed from, consists of) aramid fibers, whichmay be grouped in yarns. The aramid fibers provide increased tensilestrength to the subunit 112, and the subunit 112 may be configured tosupport short-term loads of at least 200 N. In some embodiments, aramidfibers of the first reinforcement material 122 are aligned (e.g.,generally parallel) with the optical fiber 120, not having a lay length.According to an exemplary embodiment, the aramid fibers of the firstreinforcement material 122 fully surround the optical fiber 120,separating the optical fiber 120 from the subunit jacket 116, therebyforming a barrier mitigating sticking of the optical fiber 120 to thesubunit jacket 116 during extrusion manufacturing of the subunit 112.

According to an exemplary embodiment, the second reinforcement material128 further includes aramid fibers 142 in addition to the fiberglassyarn 130. In some embodiments, the aramid fibers 142 fill the spacebetween the outer and subunit jackets 116, 124 not filled by thefiberglass yarn 130. The aramid fibers 142 of the second reinforcementmaterial 128 may be positioned between the fiberglass yarn 130 and theouter jacket 124; and in some such embodiments, the fiberglass yarn 130adjoins the indoor jacket 116 and is held tightly thereto by the hoopstress (see FIG. 1). As such, when straight and not tensioned, the fiberoptic cable 110 is structured (and the optical fiber 120 is selected)such that the optical fiber has average attenuation at 1310 nmwavelength light of 0.5 dB/km or less and at 1550 nm wavelength light of0.3 dB/km or less with environmental temperatures of the fiber opticcable 110 cycling between 60 and −30° C. per day (see, e.g., exemplarytest data provided in FIG. 6 corresponding to cycled temperature testingof the fiber optic cable 110).

According to an exemplary embodiment, the subunit 112 has essentially(e.g., substantially) no preferential bend, meaning that the subunit 112is able to bend in all directions perpendicular to the length of thesubunit 112 with the same amount of bending force. For example, in somesuch embodiments, magnitudes of forces F₁(see FIG. 2), for loading thesubunit 112 on a free end 134 thereof in a direction orthogonal to thelength of the subunit 112 and holding fixed a portion 136 of the subunit112 that is 100 mm from the free end 134 of the subunit 112 to bend thesubunit 112 between the free end 134 and fixed portion 136 thereof sothat the lengthwise center of the free end 134 of the subunit 112 isdirected 30-degrees from the lengthwise center of the fixed portion 136of the subunit 112 in any two different bend directions, differ by lessthan 25% of the magnitude of the greater of the forces F₁ for bendingthe subunit (e.g., less than 20%, less than 10%).

According to an exemplary embodiment, the second reinforcement material128, in combination with the subunit 112, is positioned or arranged suchthat the fiber optic cable 110, as a whole, has essentially no bendpreference. For example, in some such embodiments, magnitudes of forcesF₂, F₃ (see FIG. 1B), for loading the fiber optic cable on a free end138 thereof in a direction orthogonal to the length of the fiber opticcable 110 and holding a fixed portion 140 of the fiber optic cable 110that is 250 mm from the free end 138 of the fiber optic cable 110 tobend the fiber optic cable 110 between the free end 138 and fixedportion 140 thereof so that the lengthwise center of the free end 138 ofthe fiber optic cable 110 is directed 30-degrees from the lengthwisecenter of the fixed portion 140 of the fiber optic cable 110 in any twodifferent bend directions F₂, F₃, differ by less than 25% of themagnitude of the greater of the forces F₂, F₃ for bending the fiberoptic cable 110 (e.g., less than 20%, less than 10%).

In some embodiments, to achieve essentially no bend preference, thereinforcement materials 122, 128 are evenly distributed around the cable110. In other embodiments, the reinforcement materials 122, 128 mayfurther be or alternatively be formed from materials without substantialbend stiffness (e.g., fiberglass yarn 130 and aramid fiber 142).Improved flexibility and/or the lack of a preferential bend axis isbelieved to improve the maneuverability and handling qualities of thefiber optic cable 110 relative to less flexible cables and/or cableswith preferential bends. Such flexibility may allow the cable 110 topass through ducts with successive changes in direction that are notco-planar, without stressing the cable 110 and without substantialopposition to bending by reinforcement materials. In other contemplatedembodiments, a cable with rigid strength members and/or preferentialbending may incorporate features disclosed herein, such as theconstrained fiberglass 130 and subunit 112, for example.

Referring now to FIGS. 3-5, according to an exemplary embodiment thesubunit jacket 112 (see FIG. 4) is an indoor jacket including aflame-retardant jacketing material (e.g., polyvinyl chloride withfire-retardant additives), such as having a “riser” (OFNR) or “plenum”flame rating. In some embodiments, the outer jacket 124 is an outdoorjacket including medium- or high-density polyethylene, and may includeultra-violet light blocking contents. As such, the outer jacket 124provide protection for the cable 110 from outdoor elements, and removalof a section of the outdoor jacket 124 and the second reinforcementmaterial 128 converts the fiber optic cable 110 to an indoor cable(e.g., fire-rated cable). As such, the same cable 110 may be used forindoor and outdoor applications at the same time, such as routing,through the air, from a telephone pole to the side of a home, and thenfire-rated routing (without the outdoor jacket 124) through walls of thehome to computerized hardware inside the home. A splice of the opticalfiber between indoor and outdoor segments is unnecessary. In otherembodiments, the outer jacket 124 is also fire-rated, and/or the subunitjacket 120 is configured for outdoor use.

According to an exemplary embodiment, the optical fiber 120 is a single,tight-buffered optical fiber longitudinally aligned with the indoorjacket 116 and constrained by the first reinforcement material 122 suchthat the optical fiber 120 is without excess-fiber-length (e.g., lessthan 1% difference in length of the cable and length of the fiber 120).To achieve such a configuration with such a cable having components ofdifferent elasticity (e.g., aramid versus optical fiber), manufacturingof the cable 110 includes a step of tensioning the optical fiber 120while extruding the indoor jacket 116 about first reinforcement material122 and the optical fiber 120 so that the optical fiber 120 is withoutexcess fiber length following cooling and shrinkage of the indoor jacket116 after extruding the indoor jacket 116.

The tight configuration of the cable 110 of FIGS. 1-5 allows the cableto be particularly narrow. For example, in some embodiments, thetight-buffer of the optical fiber 120, the indoor jacket 116, and theoutdoor jacket 124 are each round in cross-section, and the opticalfiber 120, including the tight buffer 146 and glass core(s)/cladding 148(see FIGS. 1A & 4), has an outer diameter of less than 1 mm, the indoorjacket 116 has an outer diameter less than 3.5 mm, and the outdoorjacket 124 has an outer diameter of less than 6 mm. Accordingly, thefiber optic cable 110 is configured for installation in particularlynarrow ducts. In some such embodiments, the outdoor jacket 124 has anouter diameter of less than 5.5 mm, and may even have an outer diameterof 5 mm plus or minus 0.2 mm.

According to an exemplary embodiment, the optical fiber 120 is acommercially-available single- or multi-mode glass optical fiber, suchas one of the many types manufactured and sold by Corning Incorporated.In some embodiments, the optical fiber 120 is a multi-core opticalfiber, which includes more than one core within the same glass cladding(see, e.g., arrangement of four cores shown in FIG. 1). In still otherembodiments, the optical fiber 120 is buffered in a loose tube, asopposed to being tight-buffered, where the first reinforcement material122 adjoins the exterior of the buffer tube and the interior of thesubunit jacket 116, coupling them together. In some embodiments, thecable 110 includes more than one optical fiber, such as a ribbon of twoor more optical fibers joined together, or six optical fibers in a loosetube.

According to an exemplary embodiment, at least one of the outer jacket124 and the subunit jacket 116 includes one or more discontinuities ofmaterial 144 that provide lengthwise paths for tearing open therespective jacket 116, 124 to access the contents therein. In someembodiments, the material discontinuities 144 are formed from asecondary material that is co-extruded into the primary jacket material.For example, a polyethylene outer jacket 124 may include discontinuities144 of polypropylene (or a mixture of polypropylene and polyethylene, toimprove bonding therebetween). FIG. 5 shows the outer jacket beingpeeled open via the material discontinuities 144. In other embodiments,cables may not include discontinuities of materials, but may includeother access features, such as V-grooves to improve ease of access.

Referring to FIG. 7, a fiber optic cable 210 includes an outer jacket212 with embedded material discontinuities 214 to facilitate opening thejacket 212. The outer jacket 212 further includes embedded fiberglassyarn 216 held within the jacket 212 in an orientation and position toprovide anti-buckling strength to the jacket 212, which is intended tomitigate effects of cold-temperature shrinkage of the jacket 212. Thematerial discontinuities 214 do not overlap the embedded fiberglass yarn216 so the fiberglass yarn 216 does not interfere with tearing open thejacket 212 via the discontinuities 214. As shown, the embeddedfiberglass yarn 216 are not stranded and the material discontinuities214 extend in a straight line along the length of the outer jacket 212.

According to an exemplary embodiment, the fiber optic cable 210 furtherincludes first and second reinforcement materials 218, 220. The firstreinforcement material 218 is positioned within a subunit jacket 222 ofthe cable 210, and the second reinforcement material 220 is positionedbetween the subunit jacket 222 and the outer jacket 212, similar to theplacement of the first and second reinforcement materials 122, 128 ofthe cable 110 (see FIG. 1). According to an exemplary embodiment, thesecond reinforcement material 220 includes aramid and fiberglass yarn,while the first reinforcement material 218 only includes aramid. One ormore optical fibers may be positioned within the subunit, as disclosedwith regard to the cable 110.

Referring now to FIGS. 8-9, cables 310, 410, according to alternativeembodiments, include outer 312, 412 and subunit jackets 314, 414, aswell as first and second reinforcement material 316, 318, 416, 418. Insome embodiments, the second reinforcement material 318, 418 is embeddedin or bonded to the outer jacket 312, 412 such that second reinforcementmaterial 318, 418 remains attached to the outer jacket 312, 412 when theouter jacket 312, 412 is torn open via material discontinuities 320,420. Preferably the second reinforcement material 318, 418 is arrangedso as to be out of the way when the outer jacket 312, 412 is torn open.Tearing open the jacket 312, 412 then simultaneously controls and movesapart the second reinforcement 318, 418, which remains embedded in orbonded to the outer jacket 312, 412.

As shown in FIGS. 8-9, in contrast to FIGS. 1-7, the materialdiscontinuities 320, 420 may spiral (or otherwise revolve (e.g., S-Zpattern)) lengthwise along the outdoor jacket 312, 412 such that laylengths of the material discontinuities 320, 420 and the reinforcementmaterial 318, 418 match one another; and tearing open the jacket 312,412 then simultaneously controls and moves apart the secondreinforcement 318, 418, which remains embedded in or bonded to the outerjacket 312, 412 for accessing the indoor jacket. Fiberglass yarn 422 ofthe cable 410 is embedded in the outer jacket 412, and aramid 424 ispositioned between the outer jacket 412 and four subunits 426.

The construction and arrangements of the fiber optic cable, as shown inthe various exemplary embodiments, are illustrative only. Although onlya few embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes, and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations) without materially departing from the novel teachings andadvantages of the subject matter described herein. For example, in someembodiments glass-reinforced plastic strength members may be included ina cable as disclosed herein, such as embedded in an outer jacket. Someelements shown as integrally formed may be constructed of multiple partsor elements, the position of elements may be reversed or otherwisevaried, and the nature or number of discrete elements or positions maybe altered or varied. The order or sequence of any process, logicalalgorithm, or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes andomissions may also be made in the design, operating conditions andarrangement of the various exemplary embodiments without departing fromthe scope of the present invention.

1. A fiber optic cable, comprising: a subunit, comprising: a subunitjacket defining a passageway interior thereto, wherein the subunitjacket is an indoor jacket comprising a flame-retardant jacketing; anoptical fiber extending through the passageway; and a firstreinforcement material constraining the optical fiber within the subunitjacket such that the optical fiber and the subunit jacket are coupled toone another by way of the first reinforcement material, wherein thefirst reinforcement material is at least one of so positioned andnon-rigid in bending such that the subunit has essentially no bendpreference; and an outer portion of the fiber optic cable, comprising:an outer jacket defining an outer periphery of the cable, wherein theouter jacket is an outdoor jacket comprising medium- or high-densitypolyethylene; and a second reinforcement material between the outerjacket and the subunit jacket, whereby removal of the outdoor jacket andthe second reinforcement material converts the fiber optic cable to anindoor cable, wherein the second reinforcement material is at least oneof so positioned and non-rigid in bending such that, in combination withthe subunit, the fiber optic cable has essentially no bend preference;wherein the second reinforcement material comprises fiberglass yarn, andwherein hoop stress applied to the fiberglass yarn by the outer jacketconstrains the fiberglass yarn between the subunit and the outer jacketsuch that the fiberglass yarn is held in position and oriented toprovide anti-buckling support to the fiber optic cable and therebymitigate effects on the optical fiber of jacket shrinkage due to lowtemperatures experienced by the fiber optic cable.
 2. The fiber opticcable of claim 1, wherein the fiber optic cable has essentially nopreferential bend such that magnitudes of forces, for loading the fiberoptic cable on a free end thereof in a direction orthogonal to thelength of the fiber optic cable and holding a fixed portion of the fiberoptic cable that is 250 mm from the free end of the fiber optic cable tobend the fiber optic cable between the free end and fixed portionthereof so that the lengthwise center of the free end of the fiber opticcable is directed 30-degrees from the lengthwise center of the fixedportion of the fiber optic cable in any two different bend directions,differ by less than 25% of the magnitude of the greater of the forcesfor bending the fiber optic cable.
 3. The fiber optic cable of claim 2,the subunit has essentially no preferential bend such that magnitudes offorces, for loading the subunit on a free end thereof in a directionorthogonal to the length of the subunit and holding fixed a portion ofthe subunit that is 100 mm from the free end of the subunit to bend thesubunit between the free end and fixed portion thereof so that thelengthwise center of the free end of the subunit is directed 30-degreesfrom the lengthwise center of the fixed portion of the subunit in anytwo different bend directions, differ by less than 25% of the magnitudeof the greater of the forces for bending the subunit.
 4. (canceled) 5.The fiber optic cable of claim 1, wherein the fiberglass yarn is in theform of flattened strips positioned around the indoor jacket.
 6. Thefiber optic cable of claim 1, wherein the fiberglass yarn is strandedabout the indoor jacket at a lay length of at least 200 mm.
 7. The fiberoptic cable of claim 6, wherein the first reinforcement materialcomprises aramid fibers aligned with the optical fiber and not having alay length.
 8. The fiber optic cable of claim 1, wherein the firstreinforcement material comprises aramid fibers and the secondreinforcement material further comprises aramid fibers in addition tothe fiberglass yarn.
 9. The fiber optic cable of claim 8, wherein aramidfibers of the first reinforcement material fully surround the opticalfiber, separating the optical fiber from the indoor jacket, therebyforming a barrier mitigating sticking of the optical fiber to the indoorjacket during extrusion manufacturing of the subunit.
 10. The fiberoptic cable of claim 9, wherein the optical fiber is a single,tight-buffered optical fiber longitudinally aligned with the indoorjacket and constrained by the first reinforcement material such that theoptical fiber is without excess-fiber-length.
 11. The fiber optic cableof claim 1, wherein the second reinforcement material further comprisesaramid fibers in addition to the fiberglass yarn, and wherein aramidfibers of the second reinforcement material are positioned between thefiberglass yarn and the outdoor jacket.
 12. The fiber optic cable ofclaim 11, wherein the fiberglass yarn adjoins the indoor jacket and isheld tightly thereto by the hoop stress.
 13. The fiber optic cable ofclaim 12, wherein, when straight and not tensioned, the fiber opticcable is structured and the optical fiber is selected such that theoptical fiber has average attenuation at 1310 nm light of 0.5 dB/km orless and at 1550 nm light of 0.3 dB/km or less at temperatures of thefiber optic cable cycling between 60 and −30° C. per day.
 14. The fiberoptic cable of claim 1, wherein the tight-buffer, the indoor jacket, andthe outdoor jacket are each round in cross-section, and wherein thetight buffer has an outer diameter of less than 1 mm, the indoor jackethas an outer diameter less than 3.5 mm, and the outdoor jacket has anouter diameter of less than 6 mm, whereby the fiber optic cable isconfigured for installation in particularly narrow ducts.
 15. The fiberoptic cable of claim 14, wherein the outdoor jacket has an outerdiameter of less than 5.5 mm.
 16. The fiber optic cable of claim 14,wherein the outdoor jacket has an outer diameter of 5 mm plus or minus0.2 mm. 17-20. (canceled)
 21. A fiber optic cable, comprising: asubunit, comprising: a subunit jacket defining a passageway interiorthereto; an optical fiber extending through the passageway; and a firstreinforcement material constraining the optical fiber within the subunitjacket such that the optical fiber and the subunit jacket are coupled toone another by way of the first reinforcement material, wherein thefirst reinforcement material is at least one of so positioned andnon-rigid in bending such that the subunit has essentially no bendpreference; and an outer portion of the fiber optic cable, comprising:an outer jacket defining an outer periphery of the cable; and a secondreinforcement material between the outer jacket and the subunit jacket,wherein the second reinforcement material is at least one of sopositioned and non-rigid in bending such that, in combination with thesubunit, the fiber optic cable has essentially no bend preference;wherein the second reinforcement material comprises fiberglass yarn;wherein the fiberglass yarn is aligned with the length of the fiberoptic cable, having no lay length; and wherein hoop stress applied tothe fiberglass yarn by the outer jacket constrains the fiberglass yarnbetween the subunit and the outer jacket such that the fiberglass yarnis held in position and oriented to provide anti-buckling support to thefiber optic cable and thereby mitigate effects on the optical fiber ofjacket shrinkage due to low temperatures experienced by the fiber opticcable.
 22. The fiber optic cable of claim 21, wherein the fiberglassyarn is without a solid resin material to bind individual fibers of theyarn, but includes a non-rigid material comprising at least one of acohesive polymer and an extremely low-density, smooth, soft coating,whereby the fibers of the fiberglass yarn clump together.
 23. A fiberoptic cable, comprising: a subunit, comprising: a subunit jacketdefining a passageway interior thereto; an optical fiber extendingthrough the passageway; and a first reinforcement material constrainingthe optical fiber within the subunit jacket such that the optical fiberand the subunit jacket are coupled to one another by way of the firstreinforcement material, wherein the first reinforcement material is atleast one of so positioned and non-rigid in bending such that thesubunit has essentially no bend preference; and an outer portion of thefiber optic cable, comprising: an outer jacket defining an outerperiphery of the cable; and a second reinforcement material between theouter jacket and the subunit jacket, wherein the second reinforcementmaterial is at least one of so positioned and non-rigid in bending suchthat, in combination with the subunit, the fiber optic cable hasessentially no bend preference; wherein the second reinforcementmaterial comprises fiberglass yarn; wherein the second reinforcementmaterial further comprises aramid fibers in addition to the fiberglassyarn; and wherein hoop stress applied to the fiberglass yarn by theouter jacket constrains the fiberglass yarn between the subunit and theouter jacket such that the fiberglass yarn is held in position andoriented to provide anti-buckling support to the fiber optic cable andthereby mitigate effects on the optical fiber of jacket shrinkage due tolow temperatures experienced by the fiber optic cable.
 24. The fiberoptic cable of claim 23, wherein aramid fibers of the secondreinforcement material are positioned between the fiberglass yarn andthe outdoor jacket.
 25. The fiber optic cable of claim 24, wherein thefiberglass yarn adjoins the indoor jacket and is held tightly thereto bythe hoop stress, and wherein, when straight and not tensioned, the fiberoptic cable is structured and the optical fiber is selected such thatthe optical fiber has average attenuation at 1310 nm light of 0.5 dB/kmor less and at 1550 nm light of 0.3 dB/km or less at temperatures of thefiber optic cable cycling between 60 and −30° C. per day.